The long-term goal of this project is to elucidate basic principles of taste system function and organization. The experimental plan takes advantage of the fruit fly Drosophila as a model system, which allows powerful molecular genetic analysis and physiological measurement of individual taste cells. Understanding of insect taste may also be useful in controlling insect vectors of human disease, which receive gustatory cues from their human hosts. The project addresses the molecular and cellular logic of taste coding through three specific aims. The first aim is to construct a functional map of the taste organs, through physiological recordings from the fly's taste sensilla. This analysis should determine the number of functionally distinguishable taste sensilla and the extent to which the organization of neurons within these sensilla is stereotyped. The second aim is to elucidate the molecular underpinnings of this cellular organization by mapping individual Gr (Gustatory receptor) proteins to identified taste cells. This analysis will test the hypothesis that individual taste cells express multiple taste receptors, and that some receptors are expressed in more than one neuron per sensillum. The third aim is to identify ligands for selected Gr genes, through genetic and heterologous expression analysis. The plan is designed to investigate the tuning breadth of taste receptors, a critical issue in taste coding, and to allow further testing of the hypothesis that individual taste neurons express multiple functional receptors.